Regarding display apparatuses such as car navigation systems, touch panel devices that detect inputs made by operators touching the devices are widely known and used. In such a touch panel device, since a key touched by the operator is recognized as input information, the detection of key touch is particularly important. In a typical touch panel device, however, touch detection areas where the touch by the operator is detected are all arranged in correspondence with the sizes of indications of the respective keys. Therefore, if the touched position is out of the intended touch detection area, the touch cannot be detected.
As a solution to the above problem, there is a known technique in which the touch detection area of each key is changed on the basis of the history of key touch (see PTL 1, for example). There is another known technique in which the touch detection area of each key is gradually changed on the basis of the history of key touch (see PTL 2, for example). There is yet another known technique in which a reactive area for an inputtable key is made larger than a predetermined reactive area in a direction toward a reactive area for an uninputtable key among reactive areas for keys adjacent to the inputtable key (see PTL 3, for example).